1. Field of the Invention
The present invention relates to a reduced pressure drying apparatus. More specifically, the present invention relates to a reduced pressure drying apparatus for drying with a reduced pressure a substrate whose surface is coated with a film material.
2. Background Information
In conventional practice, films such as orientation films of liquid crystal display devices are manufactured by uniformly coating a substrate with a material for forming an orientation film (orientation film material), and drying the applied orientation film material. In a drying apparatus, for example, a substrate is held on a stage, an orientation film material is applied, and a drying cover is placed on the stage while the substrate is held in place to form an airtight space. The substrate is dried by reducing the pressure in the airtight space.
The substrate is normally coated with the solution in a uniform manner, but when an exhaust port is provided to the bottom surface of the chamber (airtight space) and air is discharged by a vacuum pump to reduce the pressure in the chamber of the drying apparatus, air bubbles sometimes form in the substrate at a portion near the exhaust port, and the applied solution expands in a localized manner. In such cases, the thickness of the resulting film becomes non-uniform, and an orientation film with a non-uniform thickness, for example, may result, which causes display defects in a liquid crystal display device. These problems of the air bubbles and localized swelling of the solution described above become even more pronounced with bigger substrates.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved drying apparatus that overcomes the problem of the conventional art. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.